1. Field of the Invention
This invention relates to an electronic component and, more particularly, to a component (balun transformer) chiefly designed to connect different electronic circuits, couple an unbalanced circuit to a balanced, and match the impedance between circuits.
2. Description of the Prior Art
As components for use in connecting electronic circuits and intended for functions such as the coupling of unbalanced and balanced circuits and impedance matching between circuits, balun transformers are known which comprise a core with flanges that define at least two recesses in between on which conductors are wound, and terminal pins set in throughholes formed in the flanges.
In FIG. 1 is shown an embodiment of such a balun transformer described in Japanese Patent Application Kokai No. 61-208913. Two conductors are wound into coils on two recesses of a flanged ferrite core 2. The flanges of the core 2 have a vertically formed throughhole each, and a total of three terminal pins 4 are inserted through the holes and fixed securely in position. Lead-out conductor ends are suitably bound around upwardly projecting ends 3 of the pins and soldered in place for connection so as to constitute a circuit similar to the equivalent circuit depicted in FIG. 11. Each winding 1 comprises, in the equivalent circuit of FIG. 11, conductors 8, 9 wound on one recess and conductors 10, 11 on the other recess. In the illustrated example the flanged core facilitates the winding operation and permits precise control of winding length, thus making it possible to avoid the dispersion of characteristic impedance. In addition, the pins 4 can be utilized for enhancing the wiring and soldering efficiencies.
FIGS. 2 and 3 illustrate an improved construction of the balun transformer of FIG. 1, disclosed in Patent Application Kokai No. 62-90911. A bar-shaped ferrite core 5 is located in contact with the flanges of a flanged core 2. The protruding ends 3 of the pins 4 are inserted into throughholes 6 also formed in the core 5, and lead-out ends of the windings are suitably bound around the further protruding ends 3 of the pins and soldered in place to provide a circuit like the one shown in FIG. 11. The cited example has further advantages that its closed magnetic circuit structure strengthens the magnetic coupling between the windings and keeps off electromagnetic influences from the outside.
It is common with the prior art devices briefly outlined above that their flanges have throughholes in which pins are set securely and the ends of windings are bound around the ends of the pins protruding from the holes as terminal pins. The structure requires intricate molds to form holes through the ferrite core and bar-shaped ferrite core alike. This, in turn, increases the part dimensions and defies efforts to decrease the number of component parts, thus weakening the competition of the product in the market.
With the spread of electronic equipment and the tendency toward miniaturization of the parts, even smaller components for planar packaging have become essential for mobile communication. In the art of communication the transmission characteristic is an important factor that governs the performance of an equipment, since it can have adverse effects upon the communication sensitivity. The present state of the components is that their characteristic has contradictory aspects. If a better characteristic is sought the component size must be larger, and if a smaller component is desired its characteristic has to be sacrificed accordingly. The balun transformer is no exception to this contradictory state. In the fields where equipment size is a major commercial consideration, small components are in wide use at the expense of characteristic.